Fun experiment with BF245-C

negative charge!

There was something about the charge inside the bag being constant.

I stopped buying surplus parts when I realized I was spending more time diagnosing part problems than design problems.

DigiKey et all really aren't that expensive compared to a day of frustration spent finding out that one's parts are out of spec.

On a sunny day (Fri, 23 Dec 2011 14:56:38 GMT) it happened snipped-for-privacy@puntnl.niks (Nico Coesel) wrote in :

negative charge!

I am sure there is, but at one point you HAVE to take one out... :-) Else just embed them in plastic.

negative charge!

Mosfets have less gate leakage. And easier to play cheap tricks with.

ftp://jjlarkin.lmi.net/2N7000.jpg

John

a negative charge!

e).

For electrometer wave-a-plastic-bag-in-the-air use, JFETs have lower input capacitance--a 2n7002's got about 50pF, a BSS138 is about half that, but a JFET's around 3pF.

So, the JFET's proportionally more sensitive. OTOH, the MOSFET will hold it longer.

I hooked an RF JFET up to an LED for some kids, and you could toggle the LED at 10 paces just scuffing your feet on the carpet. Good stuff--they loved it.

-- Cheers, James Arthur

negative charge!

The cool thing about the 2N7000 is that you can briefly connect the drain to the gate (with your fingers, whatever) and bias it partly on, right in the middle of its sensitive range. Gate leakage is not very many electrons per second. Smaller mosfets would be even better.

Add an inch or so of antenna to improve field sensitivity.

I posted some 2N7000 tricks here a while back.

I'd expect a smoke detector alpha source could do interesting things.

John

On a sunny day (Fri, 23 Dec 2011 08:24:51 -0800) it happened John Larkin wrote in :

negative charge!

This is true, but it is the nice diode in one direction that I like. I have done many projects with BF245 in the past, amps and oscillators. Very nice FET. For MOSFETS I like the dual gates. Cannot finf my dual gates and FETS anywhere, so I ordered some FETS from ebay. Arrived within just a few days from the UK...

On a sunny day (Fri, 23 Dec 2011 10:29:11 -0800) it happened John Larkin wrote in :

I am measuring alphas with a ZnS silver activated screen today, in front of the large Photonis 10 stage PMT... Last night I locked myself into a cupboard and tried looking at the flashes in a BGO crystal. Stayed there for 30 minutes for eye adaption, have seen one large one lit up the whole crystal bluish. The things one does for science, not much air there in that cupboard. LOL. The alphas will run all night tonight, as it has a low count on the Thorium fuel rods it seems, but I turned the PMT voltage way down, the flashes, when these happen are very bright, those you should be able to see with the eye. I have read somewhere the eye can see single photons (well that much light energy anyways), but BGO flashes are maybe too short to normally see (100 nS). And then all the plutonium interference. It is getting complicated.

No way you'll see single Gammas with that, the eye just isn't sensitive enough. What you saw was a cosmic ray shower, where dozens of Gammas hit the crystal at one time.

Jon

negative charge!

Oh! Wallace and Grommet! Love 'em.

a BGO crystal.

How on earth did you fit in there?

On a sunny day (Fri, 23 Dec 2011 16:31:09 -0800) it happened Joerg wrote in :

Sorry, my mistake. I sort of suspected it was the wrong word. It ment that place under the stairs to the attic, like where Harry Potter used to live. It is actually quite big.

On a sunny day (Fri, 23 Dec 2011 15:17:14 -0600) it happened Jon Elson wrote in :

Right, that is why it only happened once whilw I was there.

That would probably count as a "broom closet" although my grandma used to cure ham in there. As a kid I occasionally snuck in there, took my little toy knife and cut off a little piece where hopefully nobody would notice.

I think the Dutch word is bezemkast but some people in the south where I lived called it something like rommelkamer because of the "puinhoop" in there :-)

Actually, you were 'in the closet'. ;-)

Better than in the dog house ...

Umm... I've certainly been in the dog house from time to time, but never in the closet. I'll have to take your word for it. ;-)

Best regards, Spehro Pefhany

I've come out of the dog house, a few times in the past 40 years.

In trouble with your wife again? ;-)